Current
Current is the rate at which electric charge flows, measured in amperes (A), often called amps. In a simple closed circuit, the supply drives current through the load and back to the source. Current is not used up by a lamp: energy is transferred there. A cable current rating describes how much current it can carry in stated conditions, not how much it always carries.
Free interactive unit · electrical basics
Make the current change
Change one value, watch the circuit respond, then try three short challenges. No sign-up or equipment needed.
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This question has not yet been reviewed by a qualified electrician. It is a community draft: check anything you plan to act on against BS 7671 and your own supervisor before you rely on it. Completing it does not make you competent, certified or registered.
Arrows show conventional current direction
- Current
- 1 A
- Resistor power
- 12 W
I = V ÷ R = 12 ÷ 12 ≈ 1 A. Power P = V × I.
1–24 V · use arrow keys for one-volt steps
2–24 Ω · use arrow keys for one-ohm steps
What to notice
Start at 12 V and 12 Ω: current is 1 A. Hold resistance steady and raise voltage. Then reset and raise resistance instead. Watch how the same current reading responds differently.
Your three challenges
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Ideal DC source, fixed ohmic resistor and zero wire resistance. This model does not simulate heat, component ratings or real installations. On-screen exploration only; no XP or account progress is saved.
Read the Ohm’s law guide · Explore current · Continue on the learning path
Where Current fits in the learning path
The Career Taster section covers these units:
- The Absolute Basics
- Meet the Trade
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Read, practise, return
1. Read it in context
- Ohm's LawElectrical Science
- Cable SizingInstallation
2. Try recalling, then explore practice
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- Electrical Science — quiz previewFree · Electrical Science
- Cable Selection — quiz previewPlus · Installation
3. Return to the meaning
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Recall a related term
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The current a cable can carry continuously in its installed conditions without its insulation exceeding the temperature it was designed for. Tabulated values assume reference conditions; the real, installed capacity is what remains after correction factors for temperature, grouping and insulation have taken their share.
Current-carrying capacity
Read the Current-carrying capacity entryCompare related terms
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Current-carrying capacity — Iz
The current a cable can carry continuously in its installed conditions without its insulation exceeding the temperature it was designed for. Tabulated values assume reference conditions; the real, installed capacity is what remains after correction factors for temperature, grouping and insulation have taken their share.
Read the Current-carrying capacity entryVoltage
Voltage is the electrical potential difference between two points, measured in volts (V). It describes energy transferred per unit of charge, rather than how much charge is flowing. A battery can have voltage across its terminals even when no complete circuit exists and no current flows. Voltage and current are different quantities.
Read the Voltage entryResistance
Resistance describes opposition to current that transfers electrical energy into heat, and is measured in ohms (Ω). For an ohmic component at a fixed temperature, greater resistance means less current at the same voltage. A heating element uses resistance deliberately; cable resistance also causes heating and voltage drop. Resistance is only one part of AC impedance.
Read the Resistance entryElectrical power
Electrical power is the rate at which electrical energy is transferred, measured in watts (W) or kilowatts (kW). A 1 kW load transfers energy twice as fast as a 500 W load. In a DC circuit, power equals voltage multiplied by current. For AC loads, real power also depends on power factor, so multiplying voltage and current alone does not always give watts.
Read the Electrical power entryA definition is a start. Using it in a real question is where it sticks.